The present invention relates to an adaptive cruise control system for automotive vehicles, and particularly to an adaptive cruise control (ACC) system capable of performing transmission ratio control, engine control and/or brake control, for controlling the host vehicle""s speed and the host vehicle""s distance from a preceding vehicle, often called an xe2x80x9cinter-vehicle distancexe2x80x9d or a xe2x80x9cvehicle-to-vehicle distancexe2x80x9d.
In recent years, there have been proposed and developed various inter-vehicle distance control systems or automatic following control systems that the host vehicle (ACC vehicle) can automatically follow a preceding vehicle. Such an inter-vehicle distance control system of ten controls the inter-vehicle distance by a combination of transmission ratio control, brake control, and engine control (throttle control) in presence of preceding vehicle detection or frontal vehicular detection, and controls the host vehicle""s speed by only the engine control in absence of the preceding vehicle detection. In another type of adaptive cruise control (ACC) system having an automatic following control function, disclosed in Japanese Patent Provisional Publication No. 11-334554 (hereinafter is referred to as xe2x80x9cJP11-334554xe2x80x9d), in order to more smoothly execute the automatic following control without a feeling of physical disorder irrespective of changes in a running condition of the preceding vehicle, when switching a desired deceleration rate xcex1e of the host vehicle between a first desired deceleration rate xcex1ec suitable for a first state that the preceding vehicle is in a constant-speed running state and a second desired deceleration rate xcex1er suitable for a second state that the preceding vehicle is in a decelerating state, the system operates to gradually switch the desired deceleration rate xcex1e of the host vehicle from one of first and second desired deceleration rates xcex1ec and xcex1er to the other.
In the adaptive cruise control system disclosed in JP11-334554, concretely when the running state of the preceding vehicle shifts from the constant-speed running state to the decelerating state, a desired deceleration rate xcex1e of the host vehicle is calculated as a weighted mean of the first desired deceleration rate xcex1ec and the second desired deceleration rate xcex1er. Therefore, when shifting the constant-speed running state to a decelerating state of a comparatively small demand for deceleration, the conventional system of JP11-334554 can realize a smooth change in the deceleration rate of the host vehicle. In contrast, when shifting the constant-speed running state to a decelerating state of a comparatively large demand for deceleration, there is an increased tendency for a timing at which a decelerating operation of the host vehicle is initiated to be retarded, or there is an increased tendency for the magnitude of the deceleration rate of the host vehicle to be undesiredly reduced.
Accordingly, it is an object of the invention to provide an adaptive cruise control system for an automotive vehicle, which avoids the aforementioned disadvantages.
It is another object of the invention to provide an adaptive cruise control system, which is capable of achieve a smooth transition from one of first and second control modes (or one of an engine-torque-control-only operating mode and an engine-torque-control plus brake-control operating mode) to the other, ensuring a high control responsiveness for a demand for acceleration/deceleration and effectively suppressing changes in acceleration/deceleration of a host vehicle and.
In order to accomplish the aforementioned and other objects of the present invention, an adaptive cruise control system for an automotive vehicle, comprises a vehicle speed detector that detects a host vehicle""s speed, a man-machine interface that sets a desired host vehicle speed, a plurality of braking-and-driving force control systems that control a braking-and-driving force of the host vehicle, so that the host vehicle""s speed is brought closer to the desired host vehicle speed, and a controller configured to be electronically connected to the vehicle speed detector, the man-machine interface, and the plurality of braking-and-driving force control systems, for executing an adaptive cruise control, the controller comprising a braking-and-driving force control mode selector that selects at least one braking-and-driving force control system from the plurality of braking-and-driving force control systems, depending upon a host vehicle""s acceleration/deceleration required to bring the host vehicle""s speed closer to the desired host vehicle speed, the braking-and-driving force control mode selector selecting a first braking-and-driving force control system when the required host vehicle""s acceleration/deceleration is less than a predetermined threshold value, and selecting a second braking-and-driving force control system when the required host vehicle""s acceleration/deceleration is greater than or equal to the predetermined threshold value, and a desired host vehicle speed compensator that resets the desired host vehicle speed set at a switching point between the first and second braking-and-driving force control systems at a value being offset from the host vehicle""s speed by a predetermined value when switching between the first and second braking-and-driving force control systems occurs.
According to another aspect of the invention, an adaptive cruise control system for an automotive vehicle, comprises an inter-vehicle distance detector that detects an inter-vehicle distance between a host vehicle and a preceding vehicle, a vehicle speed detector that detects a host vehicle""s speed, a plurality of braking-and-driving force control systems that control a braking-and-driving force of the host vehicle, so that the host vehicle""s speed is brought closer to a desired host vehicle speed, and a controller configured to be electronically connected to the inter-vehicle distance detector, the vehicle speed detector, and the plurality of braking-and-driving force control systems, for executing an adaptive cruise control, the controller comprising a desired inter-vehicle distance setting section that sets a desired inter-vehicle distance from the host vehicle to the preceding vehicle, a desired host vehicle speed computation section that computes the desired host vehicle speed needed to bring the inter-vehicle distance closer to the desired inter-vehicle distance, a braking-and-driving force control mode selector that selects at least one braking-and-driving force control system from the plurality of braking-and-driving force control systems, depending upon a host vehicle""s acceleration/deceleration required to bring the host vehicle""s speed closer to the desired host vehicle speed, the braking-and-driving force control mode selector selecting a first braking-and-driving force control system when the required host vehicle""s acceleration/deceleration is less than a predetermined threshold value, and selecting a second braking-and-driving force control system when the required host vehicle""s acceleration/deceleration is greater than or equal to the predetermined threshold value, and a desired host vehicle speed compensator that resets the desired host vehicle speed computed at a switching point between the first and second braking-and-driving force control systems at a value being offset from the host vehicle""s speed by a predetermined value when switching between the first and second braking-and-driving force control systems occurs.
According to a further aspect of the invention, a method for automatically controlling at least one of a host vehicle""s speed, an inter-vehicle distance between the host vehicle and a preceding vehicle, and a relative velocity of the host vehicle to the preceding vehicle, the method comprising detecting the host vehicle""s speed, detecting the inter-vehicle distance, detecting the relative velocity, computing a first desired host vehicle speed based on a driver-selected vehicle speed, computing a second desired host vehicle speed based on the inter-vehicle distance and the relative velocity, setting a desired host vehicle speed at the first desired host vehicle speed when the preceding vehicle is absent, setting the desired host vehicle speed at the second desired host vehicle speed when the preceding vehicle is present, selecting a first braking-and-driving force control mode suitable for a first demand for acceleration/deceleration when a required host vehicle""s acceleration/deceleration is less than a predetermined threshold value, selecting a second braking-and-driving force control mode suitable for a second demand greater than the first demand for acceleration/deceleration when the required host vehicle""s acceleration/deceleration is greater than or equal to the predetermined threshold value, and resetting the desired host vehicle speed computed at a switching point between the first and second braking-and-driving force control modes at a value being offset from the host vehicle""s speed by a predetermined value when switching between the first and second braking-and-driving force control modes occurs.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.